Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, which are particularly suitable as an image pickup optical system of image pickup apparatus, such as a broadcasting television camera, a movie camera, a video camera, a digital still camera, and a silver-halide film camera.
Description of the Related Art
In recent years, a zoom lens that is small and lightweight as a whole and has a wide angle of field, a high zoom ratio, and high optical performance has been demanded for an image pickup optical system used for image pickup apparatus. As the zoom lens having the wide angle of field and the high zoom ratio, there has been known a positive-lead type five-unit zoom lens including five lens units as a whole, in which a lens unit having a positive refractive power is arranged closest to an object side. As the five-unit zoom lens, there has been known a zoom lens including, in order from an object side to an image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a negative refractive power, a fourth lens unit having a positive refractive power, and a fifth lens unit having a positive refractive power (Japanese Patent Application Laid-Open No. 2011-107693).
In Japanese Patent Application Laid-Open No. 2011-107693, during zooming from a wide angle end to a telephoto end, the second lens unit moves toward the image side, and the third lens unit and the fourth lens unit move along loci convex toward the object side. During zooming, movement loci of the second lens unit and the third lens unit are appropriately set. In this manner, a zoom lens having an imaging field angle at the wide angle end of 35 degrees to 38 degrees and a zoom ratio of 17 to 37 while reducing an effective diameter of the first lens unit and the size of the zoom lens is obtained.
The five-unit zoom lens described above is relatively easy to increase in field angle and zoom ratio. However, in order to obtain high optical performance over the entire zoom range while maintaining the increased field angle and zoom ratio, it becomes important to appropriately set the refractive powers, lens configurations, and the like of the lens units. Moreover, when an aspherical surface is used, it becomes easier to correct various aberrations, but it becomes important to appropriately set a lens unit that uses the aspherical surface, an aspherical amount thereof, and the like.
When those configurations are not appropriately set, it is difficult to provide a small zoom lens having high optical performance over the entire zoom range with a wide angle of field and a high zoom ratio. For example, in the five-unit zoom lens described above, when the lens configuration of the fourth lens unit that moves during zooming, is not appropriately set, aberration variation during zooming, especially coma in the periphery of an image plane, varies significantly, and hence it is difficult to obtain the high optical performance over the entire zoom range.